Identification of a second dynamic state during stick-slip motion.

Stick-slip, or interrupted, motion rather than smooth uninterrupted motion occurs in many different phenomena such as friction, fluid flow, material fracture and wear, sound generation, and sensory "texture." During stick-slip, a system is believed to undergo transitions between a static (solid-like) state and a kinetic (liquid-like) state. The stick-slip motion between various types of pretreated surfaces was measured, and a second, much more kinetic state that exhibits ultra-low friction was found. Transitions to and from this super-kinetic state also give rise to stick-slip motion but are fundamentally different from conventional static-kinetic transitions. The results here suggest practical conditions for the control of unwanted stick-slip and the attainment of ultra-low friction.